The proposed project is a research collaboration between the University of Texas at El Paso, The Alliance for Border Collaborative and Program Comparers to adapt, implement, and evaluate a multi-level, community-based, HIV prevention intervention (Project Encuentro). The intervention will target active heroin and crack users and consists of increasing access to HIV testing via a social network HIV testing component and reducing sexual and drug use risk via a peer network brief behavioral Intervention. Encuentro also consists of conducting community awareness meeting to target structural factors affecting HIV risk. The intervention was developed in an area severely affected by violence and stigma towards drug users, El Salvador, which makes it particularly suitable for adaptation to meet the needs of drug users living in the proposed intervention site, the U.S.-Mexico border. The proposed intervention site also has been severely affected by violence which has curtailed any prior attempts to reduce the risk drug users' HIV risk. Violence has worsened structural factors which affect HIV risk such as, increasing police persecution and stigma and reducing access to resources. In our proposed project, we will engage in formative research to understand the context of HIV risk of drug users in the border region post violence and adapt the intervention accordingly. Findings will allow us to tailor intervention components to meet the needs of drug users in the region. Subsequently, we propose to test intervention effectiveness and evaluate implementation barriers and facilitators. To accomplish our project aims we will use a mixed qualitative, quantitative approach. We will begin with a formative phase by conducting in-depth interviews with drug users (n = 40) living in the region to understand how the context of drug use risk changed as a result of the violence and will administer a social network survey (n = 200) to characterize the configuration of risk networks. Findings will yield the necessary information to culturally adapt the intervention to meet the needs of drug users in the region and will help us focus our recruitment efforts where the riskiest networks are located. After the intervention is adapted with the help of our community advisory board and our community coalition, we will implement the intervention and will assess the effectiveness and reach via 6 cross-sectional surveys administered to drug users (n=1,200). We will assess the process of implementation by conducting ethnographic field notes of all intervention activities including community engagement and CAB and coalition meetings. We will assess the fidelity and quality of the intervention. Lastly, we will conduct key informant interviews with key stakeholders involved in the project and interviews and observations will be coded to reflect key systems factors related to successful implementation of intervention components in two intervention sites (El Paso, Texas and Ciudad Juarez, Mexico). Findings will be highly significant as we will be conducting parallel research on the effectiveness of interventions shown to be effective in Latino drug users in two very different contexts: El Salvador and the U.S-Mexico border. Findings will elucidate implementation challenges and barriers and such information can then be used to assess the effectiveness of diverse implementation strategies in organizations working to serve the needs of Latino drug users.